1. Field of the Invention
The present invention relates to a combined display panel for displaying various information thereon, and more particularly to a combined display panel in which a transparent display panel is disposed on a front surface of an instrument panel; the displays on both panels are selectively shown on the combined display panel for use in, for example, an automotive vehicle.
2. Description of Related Art
A combined display panel in which a transparent electroluminescent (EL) display panel is disposed on the front surface of a usual instrument panel has been proposed hitherto. For example, Japanese Utility Model Publication No. Hei-3-17437 discloses a combined display panel which is able to display images on a transparent front panel in addition to images displayed on a conventional panel.
Japanese Patent Laid-Open Publication No. Hei-7-271310 discloses a combined display panel in which a transparent liquid crystal panel is place in front of a back panel, and displays on the front and back panels are selectively switched. In other words, images on the back and the front panels are selectively displayed.
The combined display panel shown in the former Publication is to only add the images on the front panel to the images on the back panel. The combined display panel shown in the latter Publication is able to selectively switch the images on the front panel and on the back panel. It requires, however, a light controller for switching the displays on both panels made of polymer dispersed liquid crystal and a back light for illuminating the transparent liquid crystal panel, thereby making a whole device intricate. It is conceivable to place a transparent electroluminescent panel which does not placing require the light controller in front of the back panel and selectively switching both displays. In this structure of the combined display panel, however, there is a problem that an image of the back panel is vaguely visible through the front EL panel in addition to an image of the front panel when the back panel is turned off and the front panel is turned on. This means that the back panel image, when it is not desired, interferes the front panel image. This problem is caused by the fact that light emitted from the front EL panel also reaches the surface of the back panel and is reflected thereon, and the reflected image becomes visible through the front EL panel. This phenomenon is especially notable when pointers on the back panel are made of a light reflecting body such as a fluorescent tube.